Mayor Bloomberg has instructed his aides to give him a list of people who should be laid off if he doesn’t get $600 million in union givebacks – a move that sparked outrage with union leaders.

The city’s top union negotiator called Bloomberg “immature” and “counterproductive” for the move.

In a memo sent out Friday, city Budget Director Mark Page told the head of each city agency to come up with plans “to maximize savings from layoffs.”

This comes as the two sides continue to negotiate a deal that would save the city $600 million in productivity gains. Bloomberg has repeatedly warned union leaders that layoffs will be necessary if the unions don’t make concessions.

A spokesman for the mayor said the memo “is in tandem with the $600 million in contingency cuts that went out to agency heads if labor does not do productivity savings.”

Randi Weingarten, who heads the Municipal Labor Committee, said the memo undermines the bargaining process.

“I think what they’re doing is . . . counterproductive,” she said yesterday.